The polymerization of .alpha.-monoolefins to useful thermoplastic polymer by catalysis employing coordination catalysts is well known. Coordination catalysts are used to copolymerize ethylene with many other .alpha.-olefins to prepare high molecular weight, linear, substantially crystalline polymers. When mixtures of olefins are polymerized with certain of these coordination catalysts, e.g. VOCl.sub.3 and diethylaluminum chloride, amorphous, elastomeric polymers are formed. Those copolymers made from ethylene and propylene have found wide interest and commercial usefulness. These ethylene-propylene copolymers (termed "EPR") are saturated and, thus, cannot be suflur-cured but require a peroxide or other sperical cure. Random EPR's typically contain about 30 to 70 percent weight ethylene.
EPR's are desirable rubbers because these are prepared from low-cost monomers and have good mechanical and elastic properties, as well as outstanding resistance to ozone, heat and chemical attack. One disadvantage of such polymers is their poor creep resistance. Poor creep resistance means that such polymers are deficient for applications under load. One means of improving creep resistance of EPR's is to crosslink the polymer with peroxides. However, such crosslinking is not without its associated problems such as unpleasant odors and difficult curing procedures, interference by certain stabilizers which are radical inhibitors, and removal of peroxide decomposition products.
A new ethylene/propylene polymer has now been found that does not need to be crosslinked with peroxides, since it possesses its own unique crosslinking capability.